1. Field of the Invention
The present invention relates to a sheet skew feeding correction device that performs a skew feeding correction of a conveyed sheet and an image forming apparatus such as a copying machine, a facsimile, and a printer including the sheet skew feeding correction device.
2. Description of the Related Art
A sheet fed from a cassette storing sheets therein may be skew-fed during a feeding/conveying operation due to various reasons in which a conveying roller is formed in a tapered shape or the alignment of the conveying roller is deviated from an image forming portion or a transfer portion.
Particularly, when the sheet is picked up from the cassette or the sheets are separated so that the sheets are not conveyed at the same time, the sheet may be easily skew-fed in that the roller has a narrow width or the roller does not sufficiently hold the sheet in the rotation state.
Thus, in order to obtain a satisfactory output image, there is a need to correct the skew feeding of the sheet before an image is transferred onto the sheet in the image forming portion. Further, it is effective when the correction position is near the image forming portion.
As a method of correcting the skew feeding of the sheet, there is known a general method of correcting the skew feeding by causing a sheet leading end to abut a registration roller nip. However, in the skew feeding correction method of causing the sheet leading end to abut the registration roller nip, a loss time for rotating and stopping the registration roller occurs. For this reason, a gap between the sheets which are conveyed continuously needs to be large. Thus, there is a problem in that the productivity (the number of image forming sheets per unit time) is not easily improved.
Here, although a method is practically used in which the sheet leading end abuts a shutter for the skew feeding correction without stopping the registration roller and the shutter is opened by an actuator, the damage of the sheet generated when the sheet abuts the shutter may be a problem depending on the type of sheet.
In order to solve the above-described problems, Japanese Patent Laid-Open No. 7-309481 discloses a sheet skew feeding correction device that performs a skew feeding correction by causing the sheet leading end to selectively abut any one of the registration roller nip and the shutter in response to the type of sheet.
Further, Japanese Patent Laid-Open No. 2011-190026 discloses a configuration in which the urging force of the shutter urged by a spring is switched two levels in accordance with the forward or backward rotation of the registration motor. According to this configuration, it is possible to minimize a difference in skew feeding correction caused by the different stiffness of the sheet as a big problem in the shutter urged by the spring without any loss time caused by the rotation and the stop of the registration roller.
However, in the related art disclosed in Japanese Patent Laid-Open No. 7-309481, when the sheet leading end abuts the registration roller nip, the sheet may be bitten into the registration roller nip, and hence the skew feeding correction may be not sufficiently performed.
Further, in the related art disclosed in Japanese Patent Laid-Open No. 2011-190026, a drive system that changes the spring pressure by the forward or backward rotation of the registration roller becomes complex, and hence an increase in size and cost of the apparatus occurs. Further, in recent days, the type of sheet demanded by the user increases. As a result, it is difficult to handle the type of sheet demanded by all users by the use of two levels of the urging force.